Metal shot producing method



Sept. 6, 1966 o. L. STEWART 3,270,398

METAL SHOT PRODUCING METHOD Filed May 7, 1965 :3 Sheets-Sheet 1 INVENTOR.

ORALD L. STEWART ATTORNEYS Sept. 6, 1966 o. L. STEWART 3,270,398

METAL SHOT PRODUCING METHOD Filed May 7, 1965 5 Sheets-Sheet 2 INVENTOR ORALD L, STEWART ATTORNEYS Sept. 6, 1966 o. 1.. STEWART METAL SHOT PRODUCING METHOD 5 Sheets-Sheet 5 Filed May 7, 1965 FIG. 5

INVENTOR. ORALD L. STEWART ATTORNEYS a given heat of molten means are provided of nonuniform thickness and United States Patent 3,270,398 METAL SHOT PRODUCING METHOD Orald L. Stewart, Lakewood, Ohio, assignor to The Cleveland Metal Abrasive Co., Cleveland, Ohio, a corporation of Ohio Filed May 7, 1965, Ser. No. 454,090 3 Claims. (Cl. 29148.4)

This invention concerns a method of increasing the yield of fine metal shot from a single heat of metal and a method of deforming and converting metal grit to shot for use therein. This application is a continuation-in-part of my application, Serial No, 407,432, which was filed on October 29, 1964.

In its broadest sense, the method of the invention comprises a procedure whereby the randomly sized metal shot particles produced by a single. heat of metal may be treated by breaking up the larger shot to produce fine fractured particles of shot called grit, and impacting the grit repeatedly until it is shaped into the approximate spherical shape of shot to give a larger inventory of the finer sizes of shot than are normally produced.

In the metal shot industry it has been found that -a relatively small amount of metal shot in the fines sizes, for example, from .005 to .015 of an inch in diameter,

' results from the prior art methods of pouring a heat of molten metal through a liquid jet to produce the metal shot. This fact has presented inventory problems to shot manufacturers in that at times the demand for the fine metal shot is consistently greater in relation to the demand for the larger sizes of shot which are produced in making the fine shot. Accordingly, metal shot producers have been forced, in order to meet the demands for fine shot, to produce and store larger amounts of the relatively larger sizes of shot than would otherwise be dictated by demand. Also, for this reason, the finer shot has demanded a higher price per ton on the market because of the inability of the shot producers to inexpensively produce large amounts of the fine shot from a given heat of metal.

The instant invention then is complementary to the inventory control system in that it produces a greater yield of the fine metal shot which can be sold at a higher price per ton than the larger shot.

The novel method utilizes a novel machine for converting metal grit to shot comprising a horizontally driven shaft which has elongated blade means rigidly mounted to extend radially thereabout to propel grit against an elongated target means of nonuniform thickness mounted within housing means which encloses the blades. These components are of shapes and dimensions such that the thickest portions of the target means are located on the inside of the enclosure means relatively near the path of the abrasive propelling blades. It is, of course, these portions of the target means which receive the greatest concentration of shot per square inch. Appropriate feed and collection means are provided in the machine to permit the cycling of the grit until it is impacted against the target by means of the rotating blades a sufiicient number of times to form the grit into the approximate spherical shape of shot.

By use of this novel machine in the method of this invention, an inventory of fine shot normally produced by metal being poured through a liquid bath is increased such that a higher total price per ton of the shot produced may be obtained. The target mounted with the thickest portions at the points inside of the enclosure relatively near the path of the blades in the areas of greatest concentration of fast moving shot particles so that with a minimum of material cost a long period of effective wear of the target means is accomthat-in this range a distribution of shot approximating a "ice plished. In addition to this fact, the shape of the target means insures that they may be cast in manufacturing with a directional solidification resulting which gives a porosity free target. This extends the service life of the target means considerably.

' Accordingly, it will be seen that this invention relates to the method of increasing the yield of fine metal shot from a single heat of metal by utilizing a novel machine for converting metal grit to shot which machine includes an inexpensive, cast target means which is free of porosity for long use in the method and machine combination.

The prior art has attempted many variations of production procedures to provide for an increased yield of fine metal shot for use in abrasive blasting, but none of these prior art methods have produced a fine shot in a manner which is inexpensive enough to significantly increase the supply of the fine metal shot without also creating a large amount of larger shot which must be stored or sold regardless of the demand for'it. Consequently, the manufacturers of metal shot have had inventory problems in storage of larger shot as a direct result of attempts to meet the demand for the finer and more scarce shot. By fine shot I mean shot in the neighborhood of from .005 to .015 of an inch screen size which is of substantially spherical shape.

As modern metalworking industries turn more and more to abrasive cleaning and shot peening of parts to improve the strength and appearance of cast and welded parts, the demand for clean fine abrasive shot has increased disproportionately to the demand for larger more available shot since present metal shot production methods produce only a certain small percentage of fine shot in relation to the larger shot for each heat of metal poured through a liquid bath to produce the shot. problem of obtaining a better yield of fine shot accordingly has become more critical in the industry.

It is an object of the instant invent-ion to provide a procedure which increases the yield of fine metal shot from a single heat of metal in the production of shot.

It is an additional object of the invention to provide a novel machine for converting metal grit to shot which efiiciently utilizeskinetic energy imparted to thegrit by impelling blades so that the grit is efficiently converted into the approximate spherical shape of shot so that it may be used to supplement the inventory of fine shot.

It is a further object of this invention to provide a machine for impacting grit and converting it to shot which has components capable of longer life than has been theretofore thought possible under the repeated impacting of said mate-rial.

It is still a further object of the invention to provide a novel shaped target means for use in the machine for converting metal grit to shot so as longer life for the target means within the novel machine.

It is a still further object of the invention to provide a machine which is highly effective in further rounding, polishing and removing scale and dust from already nearspherical shot to make itmore suitable for shot-peening applications.

Known compositionsand procedures for making metal abrasive shot are disclosed, for example, in the Hutcheson patent, US. Patent No. 2,670,281. As is noted in the Hutcheson patent, however, shot is obtained which ranges randomly in size from as small as .0054 inch in diameter to as-large as .156 inch in diameter. It has been found Gau-ssion curve is produced and accordingly, it is an object of the method of this'invention to enable the larger sizes of shot, thus produced, to be converted to grit and then to increased amounts of shot at the lower end of said range-particularly in the .005 to .015 range.

The

to provide better and.

The shot is usually hardened before crushing by known heat treating procedures to give it a hardness over 64 on the Rockwell C scale.

Other and more specific objects of the invention will be apparent from the detailed description to follow.

FIG. 1 illustrates the front elevational view of the novel machine for converting metal grit to shot in the novel method of this invention.

FIG. 2 illustrates a top plan view of the machine of FIG. 1.

FIG. 3 illustrates a side elevational view of the machine of FIG. 1.

FIG. 4 is a detailed fragmentary cross-sectional View taken along the line 44 of FIG. 3.

FIG. 5 is a fragmentary cross-sectional view taken along the line 5-5 of FIG. 4.

FIG. 6 is a fragmentary cross-sectional view taken along the line 66 of FIG. 5.

In the illustrated embodiment of the novel machine for converting metal grit to shot the numeral "1 generally designates the machine combination. The apparatus comprises a base 3 having legs 4 and a platform 5 upon which is mounted an electric motor 6 connected by suit able drive means 7 to a horizontal shaft 8 journaled in pillow blocks 9 and 10 on the platform 5.

The belt 7 drives the shaft 8 by means of pulleys 11 and 12 on the motor shaft 13 and the drive shaft 8. Platform 5 has an opening 15 therein through which a wear resistant enclosure of Hadfield manganese steel, or equivalent, generally designated by the numeral 20, extends. The enclosure 2tlhas a removable top cover 21 and a bottom section 22. Channel members 23 and 24 are on the right and left sides of the opening of the housing as seen in FIG. 4, for instance, such that their lower outstanding flange members 25 and 26 rest on the platform 5 extending along the opening 15. The enclosure 20 is substantially square in size and is oriented so that the corners are located at its vertical and horizontal extremes.

The horizontal drive shaft 8 extends past the pillow block 10 into the enclosure 20 through an opening 27 in the channel member 23' and the wall of the lower or bottom section 22 of the enclosure 20. A reduced diameter portion 29 is provided on the end of the shaft 8 which projects into the housing 20 for receipt of a hub member 30 which is apparently keyed to the shaft and held by means of set screw 31 to provide for rotational drive of the hub 30.

Mounted by means of bolts 33 and 34 on hub 30 are two spaced dics 35 and 36 having a plurality of blades 37 mounted therebetween as by means of set screws 39. The discs 35 and 36 are maintained in spaced relation by bridging members 38 as seen in FIG. 6. On the end of the shaft 8 and hub 30 coaxial therewith and in alignment with the blades 37 between the discs 35 and 36 is an impeller means 40 of the type well known in the centrifugal blasting machine art. The impeller 40 has an opening 41 on its side opposite the hub 30 and shaft 8 which is in direct communication with a feed tube 42 such that material flowing down the tube 42 may enter the center of the impeller 40 and be discharged out of openings 43 directly onto all of the radially innermost ends 44 of the throwing blades 37.

Appropriate seals as shown at 45 are supplied in connection with guard structures 46 and 47 mounted on the inside of the enclosure around openings 48 and 47 respectively in the enclosure 22 and beam 24 through which the gravity feed to 42 extends. Such structure is old as seen, for example, in the Rosenburger et a1. patent US. Patent No. 2,352,588, issued June 27, 1944, and acts to prevent the material being thrown from damaging the environmental structure.

Thus, it will be seen that with the material being gravity fed down the tube or conduit 42 and the shaft 8 being driven by the motor 6 of the material will be passed into d the impeller and out of the openings43 directly onto the ends 44 of the blades 37 so that centrifugal force is imparted to it to throw it from the radially outermost ends of the blades with great force.

The grit material is supplied to the feed tube 42 by means of an extension 49 thereon located directly under .a surge hopper 50'. The hopper 50 has a shape such that it is tapered in a downward direction with a valve 51 on its lower end located immediately above the feed tunnel or extension 49. Valve 51 is normally open a predetermined amount during operation.

As illustrated in FIGS. 1 and 3, the surge hopper 50 is supplied by means of a vertical conveyor 55 driven by a motor 56 through a belt 57 connected to an upper driven sprocketed drive shaft 58. Motor 56 is mounted on a suitable support '59 on top of the vertical conveyor structure 63. The conveyor 55 has individual buckets 60 and an endless belt 61 in a conventional manner and extends from the top of the surge hopper 50 to an idler pulley 62 near the base of the conveyor. A suitable structure 63 is provided to enclose and shield the conveyor 55.

At the lower end of the throwing wheel enclosure 20 is a discharge velocity control or baffle 64 to prevent the material from being thrown directly out of enclosure 20 but which permits passage of the material after it has been slowed down within the enclosure. Bafile 64 is preferably of inverted V shape to reduce wear and generally is provided with openings adjacent the walls of the enclosure 20 to permit the material to flow through an opening 65 which is flanged or otherwise suitably mounted on top of an air wash bin 66. At the lower end of the air wash bin 66 and in communication therewith is a Y valve 67 which has a straight through passage leg or conduit 68 leading to a fill hopper 70 in communication by means of gravity feed with conveyor 55 for recycling, and an angular discharge leg or conduit 69 oriented such that when the valve 67 is in the condition to close the conduit 68 to the fill hopper 70, the conduit '69 is open to act as a discharge conduit from which the treated material may be collected.

Extending laterally out of the air wash conduit 66 is a conduit 72 leading to a conventional dust collector means such that undesirable dust .and fines which are present in the air wash means 66 or passing through it by means of gravity will be sucked through an abrasive trap 73 and not be discharged into the fill hopper or be discharged out of the conduit 69 with the finished product. At the lower end of the abrasive trap 73 is a suitable pipe 74 to discharge the trapped particles. An air duct 75 applies a suction through the conduit 7'2 and abrasive trap 73 as will be readily recognized by those skilled in the art. A suitable bafile arrangement schematically illustrated as at 76 in FIG. 1 is provided to prevent the larger particles from going directly through with the dust to the conduit 75. The fine dust proceeds to a conventional bag type dust collector or other suitable collection means (not shown) in communication with conduit 75.

It will be recognized that any other suitable dust collecting arrangement can be used to clean the product after it 'has left the enclosure 22.

On the inner walls of the enclosure 20 which face the ends of the blades 37 are mounted target means 80 having sides 81 in face-to-face engagement with respective ones of the inside walls of the wheel enclosure 20. The target means 80 have faces 82 and 83 respectively mounted parallel to the axis of the shaft 8 but the faces 82 and 83 are in nonpara-llel relationship to the faces 81 in engagement with the side surfaces of the enclosure 20. This provides for a converging of the faces '81 with each of the respective faces 82 and 83 such that a tapered crosssectional structure is provided with the thickest portions of the target means 80 being located at points along the respective sides of the enclosure 20 relatively near to the path of rotation of said blades 37.

the ends of the housing wall in an area relatively near to the path of rotation of the throwing blades. The housing liner or target means 80 are secured to the inside walls of the housing 20' by bolts through suitable apertures 85 or in some other suitable manner.

The extensions of the walls of the cover 21 which are part of the lower housing section 22 have small additional target means 86 and 87 of general rectangular shape since these are in the are-as of relatively small wear due to their relatively larger distance from the rotational path of the throwing wheels 37.

In view of the function of the target means 80 in converting an'irregular shaped and abrasive metal grit into fine generally spherical shaped shot by actually cold forming the particles, it is apparent that the target must possess certain physical properties.

In this regard it is significant to note that the grit, as such, is produced by breaking up larger shot particles which have been hardened above 64 on the Rockwell C scale to provide fractured highly abrasive grit particles which are sharp and irregularly shaped and are tempered to a Rockwell hardness of from 35-55 on the C scale.

. A flat generally rectangularly shaped target was con- Q structed from an austenitic manganese steel,'-commercial-ly known as Hadfield manganese steel generally comprising about 1.0% to 1.4% carbon and from about 10% to 14% manganese and work hardenable to from 50 to 6 5 Rockwell C, and used in an apparatus such as described above for both the housing 20',and the target means 80. Operating at (1) about 2,500 rpm, (2) a circulatory rate of 25 tons per hour and (3) a capacity of 1 ton per twenty-four hour day, it was found that the target was spent in about two months.

During the course of further experimentation, other flat generally rectangular targets of the noted characteristics were prepared from alloys comprising from .30% to 1.50% silicon, from 30% to 1.50% manganese, from 6% to 18% chromium, from 1% to 4% molybdenum, from 2.5% to 4% carbon and the remainder iron; and it was found that these targets had an average life under the aforementioned operating conditions of up to six months. A particularly suitable alloy to produce a target of long life was found to-contain about .50% silicon, 50% manganese, 15% chromium, 3% molybdenum, 3% carbon and the remainder (78%) iron.

Another group of generally double wedge shaped target plates configured similarly to the target plate 80 were prepared from alloys having constituents within the above ranges and cast by techniques utilizing solidifications from the thin section to the thicker section to obtain an optimum density with negligible porosity. This group of targets was heated to approximately 1,800" F. and air cooled and had a Rockwell hardness of about 60 on the C scale. The shape of the target means becomes important because it allows directional solidification from the thinner end sections to the thicker center section giving a member having a corresponding higher density and lower porosity than members cast by other techniques.

The wedge shaped target means with alloys having from I .30% to 1.50% silicon, from 30% to 1.50% manganese, from 12% to 18% chromium, from 1.5% to 4% molybdenum, from 2.5 to 4% carbon and the remainder to 84% iron were suitable to give a life of about one year under these operating conditions. The preferred alloy, however, comprises about 35% to about .6% silicon,

from about .35 to about .6% manganese, from about 14% to 16% chromium, from about 2.5% to 3.5% molybdenum, from about 2.8% to 3.4% carbon with the remainder being iron and more particularly, an alloy comprising about 50% silicon, .50% manganese, 15% chromium, 3% molybdenum, 3% carbon and the remainder (78%) iron.

In all cases the housing 20 was constructed of Hadfield manganese steel and was found to be satisfactory because it receives substantially less abrasive particles per square inch than the target means.

It is apparent from the results obtained from these experiments that optimum target life can be obtained by the use of the particular type of alloy noted which is cast into .a wedge shaped plate by the technique of casting from the thinner sections to the thicker sections to thereby obtain optimum density and negligible porosity.

The entire apparatus may, of course, be provided with an automatic operation, for example, a storage bin for grit having. a hardness of from 40 to 45 on the Rockwell C scale as shown in the phantom in FIG. 1 and designated by the numeral 90. This storage bin may be suitably set up with a feed connection to the fill hopper 70. A suitable power operated dipper valve closing the passageway from the storage bin may be automatically controlled so as to open the bin and feed an exact amount such as one ton into the fill hopper. This may be done by known flow control methods or other flow regulating devices (not shown). After the fill hopper 70 contains the measured amount, the conveyor 55 and motor 6 start because they are in the same circuit with the valve from the storage bin. At substantially the same time, the feed gate or power operated valve from the storage bin closes.

An appropriate timer in the circuit can be present to continue the operation of the machine and recycling of the material for fifteen minutes or twenty-four hours, depending upon the time found to be needed. At the end of the time period set on the timer another power operated actuator connected to the Y-valve 67 closesthe conduit 68 and opens the valve to the discharge conduit 69 so that the one ton is discharged from the machine. The discharge valve 67 then closes, after an appropriate period of time sufficient to permit the exiting of the one ton of material and the power operated valve on the storage tank opens to feed another ton into the fill hopper. This system, of course, can be operated by merely having the valve 67 and a valve on a storage hopper being actuated by means of the timing circuit designed to perform the functions described. It is also contemplated that means continuously to convey material to the storage hopper and to take it away from the discharge 69 will be provided.

It is also true, of course, that the machine may be operated by individual manual controls or a combination of manual controls and the described automatic controls. In any event, it will be seen that the entire shot producing device could be operated for long periods of time automatically by the provision of a suitable circuit performing the described functions.

For ease of description the principles of the invention have been set forth in connection with but a single illustrated embodiment. It is not my intention that the illustrated embodiment nor the terminology employed in describing it be limiting inasmuch as variations in these may be made without departing from the spirit of the invention. Rather, I desire to be restricted only by the v scope of the appended claims.

7 8 segregating said shot into a plurality of groups by size; repeating said impacting until said grit is formed into crushing the shot of a selected size to form metal grit; the approximate shape of said shot, thereby supple segregating said grit into a plurality of groups by size; menting the inventory of fine shot produced from impactingat least one of said groups of grit against a said heat,

target; 5 and rescreening the shot to segregate the shot into a v collecting said impacted grit and impacting it against plurality of commercial size groups.

a target again; 3. The method of claim 2 which includes the step of repeating said impacting until said grit is formed into imparting a hardness of from 35 to 55 on the Rockwell the approximate shape of said shot, thereby supple- C scale to said grit before said impacting step. menting the inventory of fine shot produced from 1 said heat. 0 References Cited by the Examiner f 2. A r netlhohd (if ifncretasling the yield Of fine metal shot UNITED STATES PATENTS rom a sing e ea 0 me a compnsmg:

pouring a heat of molten metal and interrupting the 1080798 12/1913 Appwby 29 148'4 stream to produce randomly sized metal shot par- 2670281 2/1954 Hutcheson 51-309 tides, 15 2,816,466 12/1957 Gladfelter 72476 segregating said shot into a plurality of groups by size; 2398953 8/1959 Rogers 241.475 2,946,115 7/1960 F1rm 29148.4 hardening said shot to a hardness over 64 on the Rock- Well C Scale; Hanakel crushing the shot of a selected size to form metal grit; 20 3,1689% 2/1965 Harpster 241.275 3,183,080 5/1965 Harpster 75126 X segregatmg said grit into a plurality of groups by size, 04 no /1 65 E k l 29 1 22 impacting at least one of said groups of grit against 9 9 c stem at a a target;

collecting said impacted grit and impacting it against JOHN CAMPBELL Primary Examiner a target again; 25 THOMAS H. EAGER, Examiner. 

1. A METHOD OF INCREASING THE YIELD OF FINE METAL SHOT FROM A SINGLE HEAT OF METAL COMPRISING: POURING A HEAT OF MOLTEN METAL AND INTERRUPTING THE STREAM TO PRODUCE RANDOMLY SIZED METAL SHOT PARTICLES; SEGREGATING SAID SHOT INTO A PLURALITY OF GROUPS BY SIZE; CRUSHING THE SLOT OF A SELECTED SIZE TO FORM METAL GRIT; SEGREGATING SAID GRIT INTO A PLURALITY OF GROUPS BY SIZE; IMPACTING AT LEAST ONE OF SAID GROUPS OF GRIT AGAINST A TARGET; COLLECTING SAID IMPACTED GRIT AND IMPACTING IT AGAINST A TARGET AGAIN; REPEATING SAID IMPACTING UNTIL SAID GRIT IS FORMED INTO THE APPROXIMATE SHAPE OF SAID SHOT, THEREBY SUPPLEMENTING THE INVENTORY OF THE FINE SHOT PRODUCED FROM SAID HEAT. 